RFI... a couple of questions comments

[TRBTRB]

Been away from scanning for awhile, I just purchased a gre PSR 800 and I am kind of amazed at the number of sources of RFI around now. My old scanners were low band base, mobile and portable units. the last of which stopped working 5 years ago. Replacing them was always on my to do list but never got done until now. The biggest culprit seems to be my computer, I am guessing the source is the crt based monitor but could alos be the power supply. Yesterday, we were under a tornado warning and we went to the basement and I noticed that the reception was terrible. I was using a mobile magnet mount antenna which I passed up to my wife and asked her to put it on the stairs to the second floor. instead she left it on the cellar stairs right next to the wireless router. My question is this, obviously there are many new sources of RFI / EMF signals that are around now that never exisited 5 or 10 years ago can anybody help lessen the learning curve and point out some sources of possible signal interference I may not have considered?
Trent Bradbury

 

[jackj]

Almost all power supplies in today's electronic gadgets are the switching type. They rectify the AC line to produce 120-150 VDC. This DC is switched on and off at a rate of several hundred Khz and fed into a high frequency transformer to produce the low voltage the equipment needs. This scheme is much more efficient than the older style series (sometimes called linear) regulator. The problem with them is the amount of electrical noise the switching generates and radiates if they aren't properly designed. Because this type of power supply is so efficient, they can be left on 24/7. They consume almost no power if they are not supping power to their load. So anything with a clock or that can be turned on using a remote or controlled using a touch pad is powered up all the time.

Another consideration is that all digital equipment requires a clock to operate. The clock isn't to tell the time of day but is used to produce timing pulses for the digital circuits. The timing pulses are square waves that contain bunches of odd harmonics (x3, x5, x7, etc) of the fundamental clock frequency. Again, if the equipment isn't properly designed, it will radiate a lot of RF.

So the modern home is full of stuff that creates EMI. Go through your home and unplug everything, even the microwave oven. Then plug the stuff back in, one at a time, to find the culprit(s). Good luck.

 

[John_S]

RFI problems

Yes, there's more noise to deal with and this is compounded by the issue of scanner design and build. Newer scanners are generally more susceptible to RFI issues. And if I'm not mistaken, the GRE units have a hot receiver and this makes them a bit more touchy. It pays, even more so now, to maximize your signal to noise ratio... place antennas away from possible sources and up high enough to get good signal and use good quality coax that has a double shield. Computers have several sources of RF... power supplies, processors, and modems. You're not alone.

 

[TRBTRB]

Its funny the power supply on my slot car track seems to have no effect...The microwave blows away portable phones. I have not tried the cell phone near the scanner yet. Thanks for your replies.
Trent

 

[Murstech]

Unterminated cable tv cables can leak signals.

 

[kjo1981]

I am experiencing similar issues. I get interference from my computer monitor, which is actually a small Viewsonic flat-screen television. And also from my cable modem. Sometimes, the sound of the interference actually changes as I scroll through a web page or doncment on my computer. And it seems that moving the cable around for the monitor and cat-5 for the modem can either make the problem better or worse.

What can I do to reduce RFI? Would adding something like a ferrite bead to cables help alleviate some of the interference?